Two new research projects – one published this month and another that is still preliminary – suggest why some professional football players, particularly those that get concussions, may be more vulnerable to developing depression.

For both studies, researchers focused on a group of 34 retired NFL players, aged 41 to 79 and living in north Texas. The first study, published in the journal JAMA Neurology, found that former players who are depressed or cognitively impaired typically have noticeable abnormalities in a specific component of their brain known as the white matter, which is the cumulative mass of insulated nerve fibers that connect one neuron to another. In a related analysis that will be presented at the annual meeting of the American Academy of Neurology in March, players who reported a higher number of career concussions also tended to exhibit more depressive symptoms.

Together, the studies, sponsored by the BrainHealth Institute for Athletes at the Center for BrainHealth at the University of Texas at Dallas, point to changes to the brain’s white matter as a potential link between concussions and depression.

“People will sometimes want to write off a lot of depression among these [former players] with psychological explanations: They’re no longer playing, and being the center of attention, those kinds of things,” says Kyle Womack, an author on both of the studies, and an assistant professor of neurology and neurotherapeutics at the University of Texas Southwestern Medical Center. However, Womack says, the findings implicating white matter are so strong and that he believes it’s unlikely that lost social status is the primary reason for the ex-players’ grief.

In the first study, the researchers compared depression scores of 34 retired NFL players with those of 29 similar people with no history of concussion. On average, the former football players reported having experienced four concussions, and they were more likely than the people without concussions to show depressive symptoms, not just in their mood and thinking skills but in physical ways as well.

In the next study, the scientists focused on 26 of the retired players, five of whom had diagnosed depression. The researchers wanted to see if the brains of the depressed athletes looked any different than those of the non-depressed players, and used a type of MRI to image the brain and measure changes in the players’ white matter. White matter is critical for transmitting signals, “kind of like bundles of cables that are connecting different parts of the brain,” says Womack. The scan measures how much and in what directions water molecules in white matter move around. Normally, signals are passed along these fibers at high speeds, but after a concussion, when the brain is rattled inside the skull, some of these connections can stretch or tear. Such lesions can be picked up by the MRI as water leaking from the white matter rather than flowing evenly along its cables. The researchers were able to find white matter changes in the athletes showing the most cognitive impairments as measured by tests, as well as among those with higher depression scores. And when the scientists looked at just the brain scans showing white matter abnormalities, they were able to predict with 100% accuracy which scans belonged to players with depression, and with 95% accuracy which players did not.

The new studies can’t prove definitively that concussion (which is a form of traumatic brain injury) causes lasting brain changes that leads to depression. After all, not every ex-player who had concussions seemed to show later symptoms of depression. However, the links — both between the number of concussions and the number of depressive symptoms, and between the breakdown of white matter and the severity of depression — suggest that it’s worth considering depression as a possible consequence of concussions.

Neurologist Dr. John Hart, medical science director Center for BrainHealth who was involved in both studies, says the findings may have implications not just for current and former NFL players, but also for anyone with a history of concussion. That includes military veterans, victims of car crashes, or other athletes, both professional or amateur, who hit their head. Depression is manageable, he says, but only if doctors know to diagnose and treat it properly, and the results suggest that anyone with a history of concussion should be monitored for signs of depression. Left untreated, the mood disorder can lead to suicide — as was the case with linebacker Junior Seau, who played in the NFL for 20 seasons and took his own life in 2012. An autopsy report revealed his brain showed signs of chronic traumatic encephalopathy, a degenerative brain disorder linked to concussions.

The need to be alert for the signs of depression may be even more important among retired NFL players, Hart says, since many in the study were not aware that the symptoms they were having – such as lack of motivation and lethargy, or poor mood and anxiety – were signs of depression. “A lot of these players didn’t even recognize that the symptoms that they had were depression because they weren’t crying,” Hart says.

If the results are verified, they suggest that football players might be at slightly increased risk of developing depression, but detecting the condition early could help to prevent tragic consequences such as Seau’s suicide. In a statement issued through the Center for BrainHealth, Daryl Johnston, a former NFL player who took part in the studies, said “Through the Center for BrainHealth, former players can find out if there is an issue, and if you catch it early or late, there are things you can do to improve your condition. The brain is regenerative for life, and we can restore faculties that just a few years ago were thought to be lost forever.”